POV: You're an astronomer in the US who wishes for organizers to make meetings more sustainable.

Most astronomy meetings are ≤ 100 attendees in size, but depending on the meeting venue, average emissions can be very high if most people have to fly medium to long distance. For large meetings, average emissions scatter around the average value of 1t CO2e per person.

Not a big surprise, but the higher the amount of local (< 100 km from venue) participation, the smaller the average emissions. However, even meetings with few local attendees can have travel emissions below the average.

The distributions of the average CO2-equivalent emissions/person/meeting, here split for conferences and schools (since they pursue different goals for participation), show how widespread travel-related emissions are, depending on the meeting.

#Astronomy is a very internationally collaborative field, but as can be seen from the map, the majority of meetings tend to take place in Europe and North America. Meetings in remote places cause more flights → more emissions.
Our estimation is at least 42,500 tCO2e in total.

How much did astronomers actually travel in terms of distance in 2019 in total? More than 300 times to the moon and back! Or, to put it in astronomical units: more than 1.5 AU!
doi.org/10.1093/pnas...
A🧵summarizing our paper, written together with members of Astronomers for Planet Earth:

Using the Timing mode data taken by XMM-Newton, I created a PSD capable of tracing the shortest variability time scales. Most of the PSD is dominated by Poisson noise (as expected), but we also detect variability as short as 1000s, while the overall flux increase took ~16 hours.

With Mrk 421 being so bright in the X-rays, I was able to look at time-resolved spectra and analyse how they change during the flare. The blazar shows a 'harder-when-brighter' behaviour and a loop in the hysteresis curve indicates that particle cooling dominates the emission.

While the gamma-ray flare was not too exceptional (barely reaching 2 Crab Units overall - Mrk 421 has shown gamma-ray flares with the flux being larger than 3 Crab Units), the X-ray flux of Mrk 421 increased immensely within a day, which we were able to track with XMM-Newton.